Summary of production and manufacturing process for NS1402 flange

What is NS1402 alloy?

NS1402 is a universal engineering alloy that exhibits resistance to acid and alkali metal corrosion in oxidizing and reducing environments. Its high nickel content gives the alloy effective resistance to stress corrosion cracking. It has good corrosion resistance in various media, such as phosphoric acid, sulfuric acid, nitric acid, and organic acid, and alkali metals, such as potassium hydroxide, potassium hydroxide, and hydrochloric acid solution. The comprehensive performance of alloys is demonstrated in nuclear combustion dissolvers with diverse corrosive media and applied in various industrial fields where the operating temperature does not exceed 550 ℃.

With the continuous enhancement of China’s Comprehensive National Power in the 21st century, China’s manufacturing industry has also made great progress. Large forgings are increasingly valued by industry practitioners because of their important role in metallurgy, chemical industry, and other manufacturing industries. High pressure flanges are often used in high-pressure devices of petroleum pipelines and belong to large forgings. Their technical characteristics are large pipe wall thickness and small inner holes. Therefore, the mechanical properties of high pressure flanges are usually required, and strict requirements for steel smelting and heat treatment are also put forward in their production process. Currently, most of the high-pressure flange forgings in China rely on imports from developed countries. Domestic high-pressure flange forgings often have shortcomings, such as substandard quality and high cost, and their market share needs to be higher. Therefore, this article will summarize the production and manufacturing process of NS1402 flange to provide a reference for industry workers and researchers.

Manufacturing process for NS1402 flange

1. NS1402 flange raw material

The chemical composition requirements of NS1402 flanges are shown in Table 1.
The raw material is Electro-slag remelting round ingot, and the melting analysis structure is shown in Table 2.

2. Forging of NS1402 flanges

The temperature range of NS1402 alloy with low deformation resistance is above 1050 ℃, and the temperature range of good plasticity is between 1050 ℃ and 1250 ℃. The plasticity will sharply decrease when the temperature is above 1250 ℃, and the critical deformation will sharply decrease when the temperature exceeds 1200 ℃.
The decrease in critical deformation will seriously affect the plasticity of the alloy, leading to an increase in hot cracking tendency.
The initial forging temperature during forging is controlled at 1080 ± 20 ℃, the final forging temperature is greater than or equal to 850 ℃, and the heating temperature of the intermediate heat decreases by 20 ℃ in sequence. Due to the small range of forging temperature, attention should be paid to changes in forging temperature during forging, increasing the deformation of forging, and ensuring that the deformation of the last heat is greater than 30%.
Table.1 Chemical Composition Mass Fractions

Grade

C

Si

Mn

P

S

Cr

Ni

Mo

Cu

Al

Ti

Fe

NS1402

≤ 0.05

≤ 0.50

≤ 1.00

≤ 0.03

≤ 0.03

19.5-23.5

38.0-46.0

2.50-3.50

1.50-3.50

≤ 0.20

0.60-1.20

allowance

Table.2 Smelting Analytical Chemistry Composition Mass Fraction

Grade	C	Si	Mn	P	S	Cr	Ni	Mo	Cu	Al	Ti	Fe
NS1402	0.0149	0.426	0.586	0.0157	0.0005	21.12	38.48	3.22	2.19	0.101	1.13	allowance

3. Heat treatment of NS1402 flanges

The heat treatment generally includes three steps: heating, insulation, and cooling. There are many heating methods for heat treatment, among which using electricity to heat treat steel has a better effect and minimal environmental pollution. Of course, there are also other heat treatment heating methods, such as using molten salts and other substances for indirect heating. After the metal reaches the phase transition temperature, it still needs a period for the structural transformation, so it is necessary to perform a period of insulation treatment on the metal. Cooling treatment is also an important component of the metal heat treatment process, and there are many methods for cooling. The most important thing is to control the speed of metal cooling. According to the cooling rate, annealing is the slowest, normalizing is faster, and quenching is faster. However, due to the different requirements of different steel grades, the cooling methods used are also different, and the cooling rate still needs to be completely determined.
Heat treatment of metals can also be divided into four categories according to the parts that need to be treated: overall heat treatment, local heat treatment, surface heat treatment, and chemical heat treatment.
Due to the special working environment and Functional requirements of high pressure flange forgings, they have strict requirements for the purity, size, and thickness of the pipe wall of the steel used. Regarding mechanical properties, high pressure flange forgings also have high toughness and yield ratio requirements. Therefore, in addition to scientific process flow, heat treatment parameters should also be controlled.
Currently, there is no unified reference data for the heat treatment process parameters of high-pressure flange forgings, so corresponding process tests are needed to confirm the relevant process parameters.
After preliminary estimation and analysis, the heat treatment process parameters are roughly determined as follows:

• (1) Before heat treatment, the forgings are machined and heat treated in a rough machined state.
• (2) Heat treatment insulation time=heat treatment thickness × 1.1-1.5 Calculations.
• (3) The heat treatment process temperature is set to 940 ℃± 20 ℃, water-cooled.

4. Mechanical properties of NS1402 flanges

The required mechanical properties of NS1402 flanges are shown in Table 3 below.
Table.3 Requirements for Mechanical Properties of NS1402

Grade	Rm/MPa	Rp0.2/MPa	A%
	≥
NS1402	580	240	30

The mechanical performance values of the flange are shown in Table 4.
Table.4 Mechanical properties of flanges

Grade	Rm/MPa	Rp0.2/MPa	A%
NS1402	655	273	42

Summary

NS1402 is an iron nickel base high alloy material, and its Hot working performance is poor. Its Hot working has always been a difficult problem for the process. This article focuses on the forging heat treatment of NS1402 and summarizes the process of NS1402 flange forgings.
Author: Zou Qi